1. Field of the Invention
This invention relates to an optical apparatus using a motor as a drive source for moving a lens.
2. Description of the Related Art
In compensating for a defocused state of a zoom lens caused by zooming, a method for correcting focus by mechanical interlocking, for example, through a cam, has been employed. Zoom lenses are in the meantime trending to have a high magnifying rate. However, the conventional mechanical interlocking method has prevented reduction in size of a zoom lens arranged to have a high magnifying power. This problem can be solved by adopting a method of directly driving the lens for focus correction with an actuator without recourse to the mechanical interlocking. For example, some of known video cameras are arranged to use a stepping motor for focus correction and to drive with the stepping motor an optical system to a desired position determined by computation.
On the other hand, use of vibration wave motors have been put into practice to give novel features in the form of a hollow motor and a noiseless motor or the like. The vibration wave motors have come to be employed as lens driving actuators on account of these novel features.
Optical apparatuses of the kind employing a vibration wave motor as a drive source for moving a lens have been disclosed, for example, in U.S. Pat. Nos. 5,216,314, No. 5,278,935, No. 4,793,689, No. 4,660,733, No. 4,743,791, No. 4,560,263, etc.